In this experimental series we plan to test the hypothesis that endogenous prostaglandin synthesis modulates the response of the near-term ovine placental vascular bed to angiotensin II. Measurements are made using chronically catheterized near-term sheep and blood flows will be measured with radioactive microspheres. Observation of the uterine vascular response to angiotensin II will be made before and after the blockade of endogenous prostaglandin synthesis with 10 mg/kg indomethacin. Dose response curves will be constructed for uterine vascular resistance vs plasma indomethacin concentration.